-fp-accuracy is NOT a gcc option. It was added in open64 to combine the roundoff and iEEE internal options.
My point is the value of this option is a little bit counter-intuitive: "-fp-accuracy=relaxed" does NOT sound like less optimizaitons and more fp accuracy. Thanks, Min On Fri, Aug 12, 2011 at 6:10 PM, Sun Chan <sun.c...@gmail.com> wrote: > the accuracy is controlled by round_off etc, O2, O3, .. etc are tied > with roundoff, iEEE internal flags > the fp-accuracy is just a gcc option > > On Sat, Aug 13, 2011 at 6:07 AM, Min Zhao <mzhao...@gmail.com> wrote: >> Hi Ram, >> >> I was going to use -fp-accuracy option. I found it is very >> counter-initutive when "-fp-accuracy=relaxed" means less fp freedom >> but more fp accuracy. "relaxed" does not sound like improving accuracy >> at all. >> >> Can we change the setting of -fp-accuracy to be more easily >> understandable, like "strict|strict-fma|limited|relaxed"? >> >> Also, the default -O3 setting does not map to any of -fp-accuracy >> value, which seems strange to me. >> >> Thanks, >> >> Min >> >> >> On Wed, Apr 27, 2011 at 5:47 AM, Ramanarayanan, Ramshankar >> <ramshankar.ramanaraya...@amd.com> wrote: >>> Sun, >>> >>> I think my choice of words contradict with the keywords used in the flags. >>> >>> The main change here is enabling -OPT:roundoff=2 at -O3 instead of >>> -OPT:roundoff=1. This change enables fast-math functions, aggressive loop >>> nest optimizations, reassociation on floating point expressions and more >>> aggressive round-off settings. These aggressive floating point >>> optimizations improve performance when using the -O3 flag but may affect >>> floating point accuracy. The use of -fp-accuracy=relaxed in addition to -O3 >>> is recommended for cases which need more floating point accuracy. >>> -fp-accuracy=relaxed automatically sets -OPT:roundoff=1. User may also use >>> -OPT:roundoff=1. >>> >>> Please let me know if you have questions. >>> >>> Ram >>> >>> -----Original Message----- >>> From: Sun Chan [mailto:sun.c...@gmail.com] >>> Sent: Wednesday, April 27, 2011 5:02 PM >>> To: Ramanarayanan, Ramshankar >>> Cc: open64-devel@lists.sourceforge.net >>> Subject: Re: [Open64-devel] code review request for update to O3 flag >>> >>> you are really saying that to get back previous behavior, one needs to >>> -fp_accuracy=not_relaxed or something to that effect? I don't follow >>> your message. >>> Sun >>> >>> On Wed, Apr 27, 2011 at 6:37 PM, Ramanarayanan, Ramshankar >>> <ramshankar.ramanaraya...@amd.com> wrote: >>>> Could a gate keeper approve this patch? >>>> >>>> >>>> >>>> This update enhances performance of the compiled code on X8664 when using >>>> the O3 flag. Improvements come mainly from relaxing the floating point >>>> accuracy setting at O3. This enables a wide range of optimizations >>>> including >>>> loop nest optimizations and associative redundancy elimination >>>> optimizations. Given this change, users will need to use >>>> -fp-accuracy=relaxed flag in addition to -O3 if they require the earlier >>>> floating point precision. During subsequent tuning we found that the bad >>>> reference bias heuristic affects the computed cache costs and leads to >>>> incorrect choice of inner loops and is thus ignored. >>>> >>>> >>>> >>>> Following tests have been conducted with this change. >>>> >>>> >>>> >>>> 1: No compiler time failure for x86 build >>>> >>>> 2: SPEC CPU 2006 validated with AMD flags and with O3 flag >>>> >>>> 3: The gcc regression suite has no new failures on x86/Linux >>>> >>>> >>>> >>>> Best regards, >>>> >>>> Ram >>>> >>>> >>>> >>>> Ramshankar Ramanarayanan >>>> >>>> Member of Technical Staff >>>> >>>> Open Source Compiler Engineering >>>> >>>> Advanced Micro Devices, Bangalore >>>> >>>> >>>> >>>> >>>> >>>> ------------------------------------------------------------------------------ >>>> WhatsUp Gold - Download Free Network Management Software >>>> The most intuitive, comprehensive, and cost-effective network >>>> management toolset available today. Delivers lowest initial >>>> acquisition cost and overall TCO of any competing solution. >>>> http://p.sf.net/sfu/whatsupgold-sd >>>> _______________________________________________ >>>> Open64-devel mailing list >>>> Open64-devel@lists.sourceforge.net >>>> https://lists.sourceforge.net/lists/listinfo/open64-devel >>>> >>>> >>> >>> >>> >>> ------------------------------------------------------------------------------ >>> WhatsUp Gold - Download Free Network Management Software >>> The most intuitive, comprehensive, and cost-effective network >>> management toolset available today. 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